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A detailed account is given of the history, aetiology, biology, epidemiology, detection, geographical distribution, and control of huanglongbing (HLB), a destructive disease of citrus that represents a major threat to the world citrus industry, and is slowly invading new citrusgrowing areas. HLB, whose name in Chinese means \"yellow dragon disease\", was first reported from southern China in 1919 and is now known to occur in next to 40 different Asian, African, Oceanian, South and North American countries. The agent is a phloem-restricted, non cultured, Gram-negative bacterium causing crippling diseases denoted \"greening\" in South Africa, \"mottle leaf\" in the Philippines, \"dieback\" in India, \"vein phloem degeneration\" in Indonesia. The HLB bacterium belongs to the genus Candidatus Liberibacter, three species of which are currently known, Candidatus Liberibacter asiaticus, occurring in Asian countries and, to a lesser extent, in Brazil and the USA (Florida), Candidatus Liberibacter africanus with its subspecies \"capensis\", recorded from African countries, and Candidatus Liberibacter americanus present in Brazil. The suggestion is that each liberibacter species has evolved in the continent after which it is named. HLB symptoms are virtually the same wherever the disease occurs. Infected trees show a blotchy mottle condition of the leaves that results in the development of yellow shoots, the early and very characteristic symptom of the disease. Trees are stunted, declining and bear a few, small-sized, and deformed (lop-sided) fruits, that are poorly coloured (greening) and with coloration starting at the peduncular end (colour inversion). HLB can be transmitted by grafting from citrus to citrus and by dodder to periwinkle. The psyllids Trioza erytreae and Diaphorina citri are natural vectors. Two different types of HLB are known: the heat-sensitive African form transmitted by T. erytreae, which develops at temperatures of 22-25°C, and the heat-tolerant Asian form, transmitted by D. citri, which stands temperatures well above 30°C. Although the HLB pathogen can be identified by electron microscopy, other laboratory methods are used for routine detection. ELISA with monoclonal antibodies is not recommended. Better systems are dot blot hybridization with a DNA probe, and various PCR formats (one-step, nested, multiplex) using species-specific primers based on 16S rRNA or rplKAJL-rpoBC operon sequences. Because no curative methods of HLB are available, control is preventive and largely based on inoculum elimination by removal of infected trees and chemical treatments against vectors. Strict quarantine measures must be implemented to impair further international spread of HLB agents and their vectors.

Various insect bacterial associates are involved in pathogeneses caused by entomopathogenic fungi. The outcome of infection (fungal growth or decomposition) may depend on environmental factors such as temperature. The aim of this study was to analyze the bacterial communities and immune response of Galleria mellonella larvae injected with Cordyceps militaris and incubated at 15 °C and 25 °C. We examined changes in the bacterial CFUs, bacterial communities (Illumina MiSeq 16S rRNA gene sequencing) and expression of immune, apoptosis, ROS and stress-related genes (qPCR) in larval tissues in response to fungal infection at the mentioned temperatures. Increased survival of larvae after C. militaris injection was observed at 25 °C, although more frequent episodes of spontaneous bacteriosis were observed at this temperature compared to 15 °C. We revealed an increase in the abundance of enterococci and enterobacteria in the midgut and hemolymph in response to infection at 25 °C, which was not observed at 15 °C. Antifungal peptide genes showed the highest expression at 25 °C, while antibacterial peptides and inhibitor of apoptosis genes were strongly expressed at 15 °C. Cultivable bacteria significantly suppressed the growth of C. militaris. We suggest that fungi such as C. militaris may need low temperatures to avoid competition with host bacterial associates.

▪ Abstract  Nonpathogenic rhizobacteria can induce a systemic resistance in plants that is phenotypically similar to pathogen-induced systemic acquired resistance (SAR). Rhizobacteria-mediated induced systemic resistance (ISR) has been demonstrated against fungi, bacteria, and viruses in Arabidopsis, bean, carnation, cucumber, radish, tobacco, and tomato under conditions in which the inducing bacteria and the challenging pathogen remained spatially separated. Bacterial strains differ in their ability to induce resistance in different plant species, and plants show variation in the expression of ISR upon induction by specific bacterial strains. Bacterial determinants of ISR include lipopolysaccharides, siderophores, and salicylic acid (SA). Whereas some of the rhizobacteria induce resistance through the SA-dependent SAR pathway, others do not and require jasmonic acid and ethylene perception by the plant for ISR to develop. No consistent host plant alterations are associated with the induced state, but upon challenge inoculation, resistance responses are accelerated and enhanced. ISR is effective under field conditions and offers a natural mechanism for biological control of plant disease.

Over recent years, there has been a growing interest in bacteria from the genus Anaplasma, especially the species A. marginale, A. ovis and A. phagocytophilum. Anaplasmosis, a disease caused by various species of Anaplasma, is an especially important issue for animal breeders. The main vectors of these bacteria are ticks, especially the genera Ixodes, Dermacentor, Rhipicephalus and Amblyomma. The genus Anaplasma includes obligate intracellular bacteria, parasitizing in the vacuoles of cells in eukaryotic hosts. A. marginale, A. centrale, A. ovis and A. bovis are obligate intracellular bacteria parasitizing in erythrocytes and monocytes of higher vertebrates, mostly ruminants. A. platys is mainly a pathogen of canines (displaying tropism to thrombocytes) and the species A. phagocytophilum (displaying tropism to granulocytes) is pathogenic to people and domestic animals. In this paper we present characteristics and differentiation of six species of the genus Anaplasma and their vectors in the world.